The present invention relates to an active matrix-type display device, such as represented by a liquid crystal display device and an electro luminescence-type display device, provided with a plurality of pixels respectively provided with switching elements, and to a display device provided with a plurality of pixels respectively having light emitting elements such as light emitting diodes; and, more particularly, the present invention relates to a process for blanking a display image in a hold-type display device.
As a display device which holds light emitted from a plurality of respective pixels at a desired quantity for a given period (for example, a period corresponding to one frame) based on image data inputted for every frame period, a liquid crystal display device has seen increased use.
In the liquid crystal display device of the active matrix type, as shown in FIG. 27, each of a plurality of pixels PIX, which are arranged two-dimensionally or in a matrix array, includes a pixel electrode PX and a switching element SW (for example, a thin film transistor), which supplies video signals to the pixel electrode PX. In this manner, an element in which a plurality of these pixels PIX are arranged in the form of a matrix is also referred to as a pixel array 101. The pixel array 101 in a liquid crystal display device is also referred to as a liquid crystal display panel. In this pixel array 101, the plurality of pixels PIX constitute a so-called display screen which displays an image.
In the pixel array 101 shown in FIG. 27, a plurality of gate lines 10 (also referred to as scanning signal lines) extending in the lateral direction and a plurality of data lines 12 (also referred to as video signal lines) extending in the longitudinal direction (direction which crosses the gate lines 10) are respectively juxtaposed. As shown in FIG. 27, along respective gate lines 10, which are identified by addresses G1, G2, G3, . . . Gn, so-called pixel rows are formed in which a plurality of pixels PIX are arranged in the lateral direction, while along respective gate lines 12, which are identified by addresses D1R, D1G, D1B, . . . DmB, so-called pixel columns are formed in which a plurality of pixels PIX are arranged in the longitudinal direction. The gate lines 10 apply voltage signals from a scanning driver 103 (also referred to as a scanning driving circuit) to the switching elements SW, which are respectively formed on the pixels PIX constituting the pixel rows (lower sides of the respective gate lines in the case shown in FIG. 27) respectively corresponding to the gate lines 10, so as to open or close the electrical connection between the pixel electrodes PX formed on respective pixels PIX and one of the data lines 12. An operation to control a group of switching elements SW formed in a specified pixel row by applying a voltage signal from the gate lines 10 corresponding to the switching elements SW is also referred to as the selection of lines or “scanning”, and the above-mentioned voltage signal that is applied to the gate lines 10 from the scanning driver 103 is also referred to as a scanning signal.
On the other hand, to each data line 12, a voltage signal, which is referred to as a gray scale voltage or a tone voltage, is applied from a data driver 102 (also referred to as a video signal driving circuit), wherein the above-mentioned gray scale voltage is applied to respective pixel electrodes PX of the pixels PIX which constitute the pixel column (at right side of each data line 12 in FIG. 27) corresponding to each data line 12 and which are selected in response to the scanning signal.
When such a liquid crystal display device is incorporated into a television set, with respect to the period of one field of the image data (video signal) that is received, based on an interlace mode, or one frame period of video data received in a progressive mode, the above-mentioned scanning signal is sequentially applied from G1 to Gn of the gate line 10, and the gray scale voltage, which is generated based on video data received during one field period or one frame period, is sequentially applied to a group of pixels which constitute each pixel row. In each pixel, a so-called capacitive element is formed by sandwiching a liquid crystal layer LC between the above-mentioned pixel electrode PX and the counter electrode CT, to which a reference voltage or a common voltage is applied through a signal line 11, and the optical transmissivity of the liquid crystal layer LC is controlled in response to an electric field generated between the pixel electrode PX and the counter electrode CT. As mentioned above, during the operation to sequentially select the gate lines G1 to Gn one time for every field period or every frame period of the video data, the gray scale voltage applied to the pixel electrode PX of a certain pixel in a certain field period, for example, is theoretically held in the pixel electrode PX until the next gray scale voltage is received in the next field period which follows the current field period. Accordingly, the optical transmissivity of the liquid crystal layer LC, which is sandwiched by the pixel electrodes PX and the above-mentioned counter electrodes CT (that is, the brightness of the pixels having these pixel electrodes PX), is held in a given state for every one field period. A liquid crystal display device, which displays an image while holding the brightness of the pixel for every field period or every frame period in this manner, is referred to as a hold-type display device and is discriminated from a so-called impulse-type display device, such as a cathode ray tube, which causes a phosphor dot provided for each pixel perform light emission by irradiating electrons at a time when the video signal is inputted.
The video data transmitted from a television receiver set, a computer or the like has a format which corresponds to an impulse-type display device. To compare the above-mentioned driving method of the liquid crystal display device with television broadcasting, within a time which corresponds to an inverse number of the horizontal scanning frequency of the television broadcasting, the scanning signal is applied to every gate line 10, and application of the scanning signal to all gate lines G1 to Gn is completed within a time which corresponds to an inverse number of the vertical frequency. Although the impulse-type display device makes the pixels juxtaposed in the lateral direction of the screen emit light sequentially like an impulse for every horizontal scanning period in response to a horizontal synchronous pulse, in the hold-type display device, the pixel row is selected for every scanning period, as mentioned previously, a voltage signal is supplied to a plurality of pixels included in the pixel row at the same time, and, when the horizontal scanning period is finished, the voltage signal is held in these pixels.
Although the operation of the hold-type display device has been explained by taking a liquid crystal display device as an example in conjunction with FIG. 27, an electroluminescence type (EL type) display element in which the liquid crystal layer LC is replaced by an electroluminescence material, and a light emitting diode array type display device in which the liquid crystal layer LC is replaced by capacitive elements or light emitting diodes sandwiched between pixel electrodes PX and counter electrodes CT, can be operated as the hold-type display device, although they differ in operational principles (an image is displayed by controlling the injection quantity of carriers to light emitting materials in these devices).
Here, for example, a hold-type display device displays an image by holding the brightness of respective pixels for the above-mentioned frame period. Accordingly, there may be a case such that, when a display image is replaced with a different display image between a pair of continuous frame periods, the brightness of the pixels does not sufficiently respond.
This phenomenon is due to the fact that the pixel which is set to given brightness in a certain frame period (for example, a first frame period) holds the brightness corresponding to the first frame period until the pixel is scanned in the next frame period (for example, a second frame period) which follows the first frame period. This phenomenon is also based on a so-called hysteresis of the video signal in each pixel, wherein a portion of the voltage signal (or a quantity of charge corresponding to the voltage signal) which is transmitted to the pixel during the first frame period interferes with the voltage signal (or a quantity of charge corresponding to the voltage signal) which is to be transmitted to the pixel during the second frame. Techniques which solve these problems related to the responsiveness of the image display in the display device using the hold-type light emission, for example, are disclosed in JP-B-06-016223, JP-B-07-044 670, JP-A-05-073005, and JP-A-11-109921, respectively.
Of these publications, JP-A-11-109921 discusses a so-called blurring phenomenon which occurs at the time of reproducing an animated image by a liquid crystal display device (an example of a display device using the hold-type light emission). Here, the blurring phenomenon is a phenomenon which makes a profile of an object obscure, compared to a cathode ray tube, which makes pixels emit light like an impulse. To solve this blurring phenomenon, JP-A-11-109921 discloses a liquid crystal display device in which one pixel array (a group consisting of a plurality of pixels arranged two-dimensionally) of a liquid crystal display panel is divided into two divided pixel arrays at upper and lower portions of the screen (image forming region) and data line driving circuits are respectively provided for these divided pixel arrays. The liquid crystal display device performs a so-called dual scanning operation in which, by selecting one gate line from each of the upper and lower pixel array, that is, by selecting two gate lines in total, a video signal is supplied from the data line driving circuits formed in respective pixel arrays. While performing this dual scanning operation in one frame period, the vertical phase is shifted so as to input a signal corresponding to a display image (a so-called video signal) to one pixel array from the data line driving circuit and a signal of a blanking image (a black image, for example) to another pixel array from the data line driving circuit, respectively. Accordingly, it is possible to provide a period for performing an image display and a period for performing a blanking display at both upper and lower pixel arrays during one frame period, and, hence, the period that the video is held as a whole can be shortened. Due to such a constitution, even in a liquid crystal display device, it is possible to obtain an animated image display performance that is comparable to that of a cathode ray tube.
JP-A-11-109921 discloses a technique in which one liquid crystal display panel is divided into upper and lower pixel arrays, the data line driving circuits are respectively provided for the divided pixel arrays, one gate line for each of upper and lower pixel arrays, that is, two gate lines in total, are selected, the display region, which is divided into upper and lower regions, is subjected to dual scanning by respective driving circuits, and the blanking image (the black image) is inserted by shifting the vertical phase during one frame period. That is, by enabling one frame period to assume the video display period and the blanking period therein, it is possible to shorten the image holding period. Accordingly, with the use of a liquid crystal display, it is possible to obtain animated image display characteristics of the impulse-type light emission, as in the case of a cathode ray tube.